A major technical obstacle to the widespread use of hydrogen (H2) as a nonpolluting fuel for cars is the lack of a safe and efficient system for on-board storage.[1] Of the many potential solutions being investigated,[2] an attractive possibility is a system based on the reversible adsorption of H2 on the internal surface of a microporous material such as a zeolite,[3] carbon,[4] or metal-organic framework (MOF).[5, 6] At present, the quantity of H2 that can be adsorbed onto any type of microporous material falls below the requirements of a practical H2 storage system. Hence, there is an urgency to develop materials which can be tailored to provide a structure [7, 8] and chemical composition [9] suitable for the specific demands of H2 physisorption. Previously, organic polymers have not been considered as materials for the storage of hydrogen because polymers generally have enough conformational and rotational freedom to pack space efficiently and thus do not offer high surface areas. However, the recently reported polymers of intrinsic microporosity (PIMs) are composed wholly of fusedring subunits designed to provide highly rigid and contorted macromolecular structures that pack space inefficiently. Hence they form solids with large amounts of interconnected free volume, providing accessible internal surface areas in the range 500–900 m2 gÀ1.[10, 11] PIMs are prepared by using a benzodioxane formation reaction between suitable monomers, one of which must contain a site of contortion such as a spiro-center or a rigid nonplanar unit. A PIM can be prepared either as an insoluble network or as a soluble polymer, suitable for solution-based processing, depending upon the number of catechol and aromatic ortho-dihalide groups possessed by the monomers. For example, a soluble PIM (PIM-1) is prepared from the reaction between 5, 5’, 6, 6’-tetrahydroxy-3, 3, 3’, 3’-tetramethyl-1, 1’-spirobisindane and tetrafluoroterephthalonitrile, whereas, a network-PIM (HATN-network-PIM) is formed from the reaction between the same readily available spiro-cyclic bis (catechol) monomer and hexachlorohexaazatrinaphthylene (Scheme 1).[11, 12] PIM-1 can be cast from solution to form robust microporous selfstanding films that show excellent promise for gas [13] and solution phase membrane separations.[11] The HATN-network-PIM has in-built ligands for metal complexation and the PdII-loaded material is proving an excellent heterogeneous catalyst for Suzuki aryl–aryl coupling reactions.[12] In the context of hydrogen adsorption, we believe that PIMs may offer an attractive combination of properties including low intrinsic density (they are composed of only light elements—C, H, N, O—a real advantage over MOF materials),[14] chemical homogeneity (an advantage over carbons), thermal and chemical stability, and synthetic reproducibility. Of particular interest is the potential to tailor the micropore structure by choice of monomer precursors, for example, by the use of monomers that contain pre-formed cavities to provide sites of an appropriately small size for hydrogen adsorption. To investigate this possibility, the bowl-shaped receptor monomer, cyclotricatechylene (CTC),[15] was incorporated within a network-PIM by using